Statement of the Prior Art--The sulfur-ammonia method for scrubbing hydrogen sulfide from coke oven gas is described in U.S. Pat. No. 3,789,105. In this sulfur-ammonia method, hydrogen sulfide is removed from the coke oven gas in a hydrogen sulfide stripper by washing with ammoniacal wash water. Thereafter ammonia is recovered from the washed coke oven gas by washing with water in an ammonia stripper. The effluent wash water from the hydrogen sulfide stripper is treated in a deacidifier with ammonia water to release the hydrogen sulfide as a gas which is recovered for subsequent use, e.g., in a sulfuric acid generator. The effluent wash water from the deacidifier is introduced into the hydrogen sulfide stripper as a portion of the ammoniacal wash water. A further improvement in the sulfur-ammonia method provides an absorber for hydrogen sulfide gas. The absorber is employed in those instances when the hydrogen sulfide gas cannot be delivered for processing, e.g., when the following sulfuric acid generator or other plant for processing the hydrogen sulfide gas is out of action. In such instances the hydrogen sulfide vapors are washed in the absorber with coal water to produce a "strong liquor" containing dissolved hydrogen sulfide. The "strong liquor" is in part recycled through the scrubbing tower and in part withdrawn to a "strong liquor" storage facility. The clean gases from the absorber are returned to the hydrogen sulfide scrubber along with coke oven gas. In normal operation of the sulfur-ammonia method, the concentrator is not active but instead is provided for use only during abnormal conditions when the hydrogen sulfide gas stream cannot be directly processed.
One of the shortcomings of this installation is that the concentrator is not employed during the normal operation of the plant.